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Laboratory Safety Incidents: Electrical Shock
Common Equipment (top)
Melted Down Surge Protector
Surge Protector, a description of an incident and explanatory material by the West Whiteland Fire Company of Exton, PA
Electrocution Due to Improper Use of Common Equipment (top)
Key Instruction Points:
1)Generally, equipment used in research should have a 3 prong plug or be double insulated. Equipment with neither of these features are less safe but may meet electrical codes. A 3 prong plug must always go into a 3 prong outlet. Do not use a "cheater" plug or pull out the 3rd prong.
2) Do not use multiple cube taps in a standard outlet. If you must plug more than two pieces of low demand equipment into a standard outlet, use a fused power strip that will trip if too much power is used.
3) Make sure that any outlet near a sink or other water source is Ground Fault Circuit Interrupter (GFCI) protected. If you have a GFCI, periodically test it by plugging something into it and pushing the "test" button. The equipment should turn off. Then turn it back on.
4) Do not disable any electrical safety feature expecting that another safety feature will protect you. In the incident described below, if proper lamps were used, the ballast could still have been defective from other causes. Also, GFCIs can be defective. That is why they should be periodically tested.
Dr. X was electrocuted in his laboratory at Y.
Background
Dr. X was conducting an experiment related to plant growth. He needed to expose the plants to light for specific time-periods each day. Accordingly, he had a portable fluorescent lighting rack constructed and mounted on a wooden frame. He also obtained an electric timer to automatically turn the lights on and off. The light fixture was plugged into the timer, which was plugged into the wall outlet. However, since the timer only accepted a two prong plug, an adapter was used to allow the three prong plug of the lighting rack to be used with the two prong outlet of the timer.
The Incident
Dr. X adjusted the timer so that the lights would be on and plugged the timer into a standard 3-prong wall outlet. Then another person in the lab noticed Dr. X grasping the lighting rack and appearing to be rigid. A third person grasped Dr. X by the shoulders and pulled him away from the lighting rack. CPR was performed on him until EMS arrived. Dr. X was transported to a hospital where he was pronounced dead.
The Investigation
The investigation revealed the following details:
*A potential difference of 397 volts was measured between the metal fluorescent light fixture and the adjacent stainless steel sink. (There should not have been any potential ifference).
*Both the fixture and the wall outlet were found to be wired correctly.
*The light fixture was rated for 800 mA, but the lamps used were 1500 mA.
*The transformer in the ballast was found to have short circuited to the case.
What Probably Happened
Use of bulbs drawing more current than approved for the fixture caused overheating of the ballast resulting in melting of insulation around the transformer coil. This allowed an energized transformer wire to touch the metal cover of the ballast which in turn energized the metal fluorescent fixture. The lights probably continued to function since they were wired correctly.
When Dr. X grasped the fixture, some part of him probably brushed against the nearby metal sink. This completed a circuit to ground through Dr. X, electrocuting him.
Preventing this Fatality
As with many very serious accidents, a number of factors were involved, any one of which could have prevented this fatality.
-If overrated lamps had not been used, the ballast would probably not have overheated and failed.
-If the ground wire connection between the light fixture and the plug not been interrupted by the "cheater" adapter and the two-prong timer, the fixture would have safely shorted to ground tripping the circuit breaker when the equipment was plugged in before Dr. X touched it.
-Had the standard outlet near the sink been Ground Fault Circuit Interrupter (GFCI) protected (as it should have been because it was near a sink), the GFCI would have tripped at the first flow of current through Dr. X immediately cutting off power to the fluorescent fixture and saving his life.
These electrical safety violations cost Dr. X his life. If any one of them had been corrected before the incident, Dr. X would still be researching plant growth.
What can I do to prevent something like this from happening in my lab?
1)Follow manufacturer's recommendations for use of electrical equipment. Do not use electrical equipment for a task it is not designed for.
2) Generally, equipment used in research should have a 3 prong plug or be double insulated. Equipment with neither of these features are less safe but may meet electrical codes. A 3 prong plug must always go into a 3 prong outlet. Do not use a "cheater" plug or pull out the 3rd prong.
3) Do not use multiple cube taps in a standard outlet. If you must plug more than two pieces of low demand equipment into a standard outlet, use a fused power strip that will trip if too much power is used.
4) Make sure that any outlet near a sink or other water source is Ground Fault Circuit Interrupter (GFCI) protected. If you have a GFCI, periodically test it by plugging something into it and pushing the "test" button. The equipment should turn off and then turn it back on.
5) If you see a person being electrocuted, DO NOT TOUCH HIM! The electricity can go though you too. If possible, remove the power (pull plug or trip circuit breaker), or use a non-conductive item (e.g. wooden broom handle) to pry him away from the contact.
6) Above all, do not disable any electrical safety feature expecting that another safety feature will protect you. In the incident described above, if proper lamps were used, the ballast could still have been defective from other causes. Also, GFCIs can be defective. That is why they should be periodically tested.
7) Check that power cords are in good condition.
8) Do not use extension cords as a substitute for permanent wiring.
Electrophoresis
(top)
Electrical Shock from Electrophoresis Unit (top)
Key Instruction Points:
1. Do not work around energized, exposed
conductors.
A laboratory worker received a potentially fatal
electrical shock when he accidentally touched a high voltage electrical connector on an
electrophoresis device. The contact points were on the right elbow and right knee. Had one
of the contacts been on the opposite side of the body, the shock could have been fatal.
The primary cause of this incident was the existence of an exposed high voltage conductor
in the form of a stackable banana plug at the device. When connected to the male plug on
the device, the male connector plug was left exposed with no insulation or guarding.
The accident could have been avoided by eliminating all
exposed conductors in connector cords and electrophoresis devices by either
-fitting each electrophoresis with its own set of
permanently attached connector cords to eliminate jacks and plugs entirely at this point;
or
-eliminating cords with stackable plugs on both ends by
replacing the stackable plugs on one end with a female only jack (all electrophoresis
devices should be fitted with male only plugs).
Lasers (top)
Electrical Shock from Laser Power Supply
(top)
Key Instruction Points:
1. Do not defeat machine safety interlocks.
2. Do not work around energized, exposed
conductors.
A laboratory worker noticed condensation on the high voltage power
supply for a high powered laser. With the power still on, he wiped the moisture with a
tissue, making contact with the exposed anode terminal at approximately 17,000 volts DC to
ground.
He received a severe electrical shock and second degree burns to his right thumb and
abdomen. Witnesses stated that they heard a loud "snap" and then heard the
laboratory worker scream and stagger out to the hallway. He was immediately met by a
secretary, and told her "I got a shock" as he collapsed into her arms and onto
the floor. He had no pulse and was not breathing. Public Safety officers were nearby and
immediately started CPR. The ambulance crew arrived and was able to restore his heartbeat
using a defibrillator.
Fortunately, the laboratory worker lived to tell his story. He said that he knew that the
power was on but was not aware that contact was possible at the high voltage terminals.
The interlocks had been defeated and guards removed with no alternate guarding or
precautions taken.
Understand the operating characteristics of equipment before use. Do not defeat
machine safety interlocks.
Do not work around energized exposed conductors.
Revision Date: 12/31/2006
url: http://www2.umdnj.edu/eohssweb/aiha/accidents/electrical.htm
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